Electronic device with switched-capacitor tuning and related method

ABSTRACT

A device comprises a first variable capacitance block comprising four first capacitors, a second variable capacitance block comprising four second capacitors, wherein the second capacitors are arranged in a same configuration as the first capacitors, a third variable capacitance block comprising four third capacitors, a fourth variable capacitance block comprising four fourth capacitors, and wherein the fourth capacitors are arranged in a same configuration as the third capacitors, a first switch coupled between the first variable capacitance block and the second variable capacitance block, a second switch coupled between the third variable capacitance block and the fourth variable capacitance block, a third switch coupled between the first variable capacitance block and the fourth variable capacitance block and a fourth switch coupled between the third variable capacitance block and the second variable capacitance block.

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/902,392, filed May 24, 2013, and entitled “Electronic Devicewith Switched-Capacitor Tuning and Related Method,” which claimspriority to U.S. Provisional Application Ser. No. 61/748,681, filed onJan. 3, 2013, entitled “Electronic Device with Switched-Capacitor Tuningand Related Method,” which applications are hereby incorporated hereinby reference.

BACKGROUND

The semiconductor industry has experienced rapid growth due toimprovements in the integration density of a variety of electroniccomponents (e.g., transistors, diodes, resistors, capacitors, etc.). Forthe most part, this improvement in integration density has come fromshrinking the semiconductor process node (e.g., shrinking the processnode towards the sub-20 nm node). As device dimensions shrink, voltagenodes also shrink, with modern core device voltages trending toward lessthan 1 Volt, and input/output (I/O) device voltages under 2 Volts.

Many types of analog, digital and mixed-signal circuits rely on tuningnetworks to achieve fine granularity in performance metrics, such asgain, bandwidth, center frequency, oscillation frequency, and the like.The tuning networks are often designed with a view to increaseresolution while maintaining or shrinking area and also guarding againstprocess, voltage, and temperature (PVT) variation.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a circuit diagram of an electronic device in accordance withvarious embodiments of the present disclosure;

FIG. 2 is a diagram of the variable capacitor network in accordance withvarious embodiments of the present disclosure;

FIG. 3 is a diagram of a variable capacitor in accordance with variousembodiments of the present disclosure;

FIG. 4 is a diagram of the variable capacitor having the firstcapacitance in accordance with various embodiments of the presentdisclosure;

FIG. 5 is a diagram of the variable capacitor having the secondcapacitance in accordance with various embodiments of the presentdisclosure;

FIGS. 6 and 7 are diagrams of switch circuits in accordance with variousembodiments of the present disclosure;

FIGS. 8, 9, 10 and 11 are diagrams of operating modes of the switchcircuits in accordance with various embodiments of the presentdisclosure;

FIG. 12 is a flowchart of a method of operating an electronic devicewith switched-capacitor tuning in accordance with various embodiments ofthe present disclosure;

FIG. 13 is a circuit diagram of a digitally-controlled oscillator (DCO)in accordance with various embodiments of the present disclosure;

FIG. 14 is a flowchart of a method of designing an electronic devicewith switched-capacitor tuning in accordance with various embodiments ofthe present disclosure;

FIG. 15 illustrates a diagram of a variable capacitor in accordance withvarious embodiments of the present disclosure;

FIG. 16 illustrates a schematic diagram of the variable capacitor shownin FIG. 15 in accordance with various embodiments of the presentapplication;

FIG. 17 illustrates a schematic diagram of the variable capacitor havingthe first capacitor in accordance with various embodiments of thepresent disclosure; and

FIG. 18 illustrates a schematic diagram of the variable capacitor havingthe second capacitor in accordance with various embodiments of thepresent disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments will be described with respect to a specific context, namelyan electronic circuit with switched-capacitor tuning, and the like.Other embodiments may also be applied, however, to other types ofanalog, digital, or mixed-signal circuits.

Throughout the various figures and discussion, like reference numbersrefer to like components. Also, although singular components may bedepicted throughout some of the figures, this is for simplicity ofillustration and ease of discussion. A person having ordinary skill inthe art will readily appreciate that such discussion and depiction canbe and usually is applicable for many components within a structure.

Analog, digital, and mixed-signal circuits are characterized by certainperformance metrics, such as gain, direct current (DC) offset,bandwidth, center frequency, oscillator frequency, resolution, noiserejection, power consumption, and the like. Nearly every type ofperformance metric is controllable through proper circuit design.Constraints on circuit area and power consumption can impose trade-offsbetween the performance metrics defined for a circuit, such as anamplifier, a filter, a phase-locked loop (PLL), an analog-to-digitalconverter (ADC), a digital-to-analog converter (DAC), or the like. Inmany applications, tuning networks are included either to fine-tune aperformance metric prior to shipping a final product, or to select anappropriate level for the performance metric on-the-fly. One example ofthe former would include a tunable bias circuit, such as a tunablecurrent mirror, that tunes a low noise amplifier (LNA) for noise figureor input-referred third-order intercept point (IIP3). An example of thelatter would be a variable capacitor used in an LC tank circuit fordigitally controlling oscillation frequency of the LC tank circuit.

In the following disclosure, a novel electronic device withswitched-capacitor tuning is introduced. The electronic device uses aswitched-capacitor variable capacitance network to improve performance(e.g., resolution, PVT variation) of a circuit of the electronic devicewhile maintaining low area. The circuit in conjunction with theswitched-capacitor variable capacitance network exhibits highresolution, precise capacitance, and small area.

FIG. 1 is a circuit diagram of an electronic device 10 in accordancewith various embodiments of the present disclosure. The electronicdevice 10 includes a circuit 100 and a variable capacitance network 110.In some embodiments, the circuit 100 has an input terminal for receivinga first signal S1, and an output terminal for outputting a second signalS2. In some embodiments, the variable capacitance network 110 has afirst terminal electrically connected to a first internal node of thecircuit 100, and a second terminal electrically connected to a secondinternal node of the circuit 100. In some embodiments, the firstterminal is an inverting output terminal, and the second terminal is anon-inverting output terminal.

The circuit 100 is an analog circuit, a digital circuit, a mixed-signalcircuit, a combination thereof, or the like. In some embodiments, thecircuit 100 is a digitally-controlled oscillator (DCO) used with anall-digital phase-locked loop (ADPLL). In some embodiments, the circuit100 is a filter. In some embodiments, the circuit 100 is a radiotransceiver, an amplitude modulator, an analog-to-digital converter(ADC), an impedance matching network, a programmable gain amplifier, orthe like.

FIG. 2 is a diagram of the variable capacitor network 110 in accordancewith various embodiments of the present disclosure. The variablecapacitor network 110 includes variable capacitors 111, 112, . . . , 113electrically connected in parallel. Number N of the variable capacitors111, 112, . . . , 113 is a positive integer. The variable capacitor 111is described as an example. In some embodiments, capacitance of thevariable capacitor 111 is switchable between a first capacitance and asecond capacitance. In some embodiments, the first capacitance is lessthan the second capacitance. A difference between the second capacitanceand the first capacitance is a capacitance delta (ΔC). In someembodiments, a single control signal is used to select the firstcapacitance or the second capacitance. The single control signal has atleast two states, e.g. logic high or logic low, binary one or binaryzero, on or off, or the like. In some embodiments, a first controlsignal and a second control signal are used to select the firstcapacitance or the second capacitance. The first control signal isinverse of the second control signal. When the first control signal islogic high, for example, the second control signal is logic low. Whenthe first control signal is logic low, the second control signal islogic high. Other variable capacitors 112, . . . , 113 are operatedsimilarly to the variable capacitor 111.

In some embodiments, first capacitances of the variable capacitors 111,112, . . . , 113 are different (e.g., binary code, gray code), andsecond capacitances of the variable capacitors 111, 112, . . . , 113 aredifferent (e.g., binary code, gray code). For example, the firstcapacitance of the variable capacitor 111 may be 16*C, and the firstcapacitance of the variable capacitor 112 may be 8*C, where C is a unitcapacitance. In some embodiments, the first capacitances of the variablecapacitors 111, 112, . . . , 113 are the same (e.g., thermometer code),and the second capacitances of the variable capacitors 111, 112, . . . ,113 are the same (e.g., thermometer code). In some embodiments, variablecapacitors representing upper bits (e.g., most significant bits (MSBs))of the variable capacitor network 110 have binary coded capacitances,and lower bits (e.g., least significant bits (LSBs)) of the variablecapacitor network 110 have thermometer coded capacitances. In someembodiments, the capacitance deltas (ΔC) of the variable capacitors 111,112, . . . , 113 are thermometer-coded, binary-coded, hybrid-coded, orthe like.

Total capacitance of the variable capacitor network 110 is equal to thesum of the individual capacitances of the variable capacitors 111, 112,. . . , 113. In some embodiments, a baseline capacitance C_(min) of thevariable capacitor network 110 is equal to the sum of the firstcapacitances of the variable capacitors 111, 112, . . . , 113. In someembodiments, a maximum capacitance C_(max) of the variable capacitornetwork 110 is equal to the sum of the second capacitances of thevariable capacitors 111, 112, . . . , 113. Resolution of the variablecapacitor network 110 is determined by number and type of bits of thevariable capacitors 111, 112, . . . , 113. For example, 64 discretecapacitances may be represented by 64 capacitor deltas having thethermal-coded capacitances (e.g., ΔC, ΔC, ΔC, . . . , ΔC), 6 capacitordeltas having binary-coded capacitances (e.g., 32*ΔC, 16*ΔC, 8*ΔC, 4*ΔC,2*ΔC, 1*ΔC), or 7 capacitor deltas having hybrid-coded (binary andthermal) capacitances (e.g., 32*ΔC, 16*ΔC, 8*ΔC, 4*ΔC, ΔC, ΔC, ΔC),where ΔC is a unit capacitance delta (e.g., 10 attofarads).

FIG. 3 is a diagram of a variable capacitor 311 in accordance withvarious embodiments of the present disclosure. The variable capacitor311 is an example of one type of variable capacitor that is used in someembodiments for the variable capacitors 111, 112, . . . , 113. A firstterminal of a first capacitor 121 is electrically connected to a node 31(e.g., a node OUT+ shown in FIG. 2). A second terminal of the firstcapacitor 121 is electrically connected to a node 11. The firstcapacitor 121 has a first capacitance CA (e.g., 1 femtofarad). A firstterminal of a second capacitor 122 is electrically connected to a node32 (e.g., a node OUT-shown in FIG. 2). A second terminal of the secondcapacitor 122 is electrically connected to a node 12. In someembodiments, the second capacitor 122 has the first capacitance CA. Insome embodiments, the second capacitor 122 has a different capacitancethan the first capacitor 121. A first switch 131 has a first terminalelectrically connected to the node 11. A second terminal of the firstswitch 131 is electrically connected to the node 12. In someembodiments, the first switch 131 is controllable by an electricalsignal. In some embodiments, the first switch 131 is an N-typemetal-oxide semiconductor (NMOS) transistor, a P-typemetal-oxide-semiconductor (PMOS) transistor, a pass gate, or the like.When the first switch 131 is closed (turned on, short-circuited), thesecond terminal of the first capacitor 121 is electrically connected tothe second terminal of the second capacitor 122. When the first switch131 is open (turned off, open-circuited), the second terminal of thefirst capacitor 121 is electrically isolated from the second terminal ofthe second capacitor 122.

A first terminal of a third capacitor 123 is electrically connected tothe node 31. A second terminal of the third capacitor 123 iselectrically connected to a node 13. The third capacitor 123 has asecond capacitance CB (e.g., 1.2 femtofarads). A first terminal of afourth capacitor 124 is electrically connected to a node 32. A secondterminal of the fourth capacitor 124 is electrically connected to a node14. In some embodiments, the fourth capacitor 124 has the secondcapacitance CB. In some embodiments, the fourth capacitor 124 has adifferent capacitance than the third capacitor 123. A second switch 132has a first terminal electrically connected to the node 13. A secondterminal of the second switch 132 is electrically connected to the node14. In some embodiments, the second switch 132 is controllable by anelectrical signal. In some embodiments, the second switch 132 is anN-type metal-oxide semiconductor (NMOS) transistor, a P-typemetal-oxide-semiconductor (PMOS) transistor, a pass gate, or the like.When the second switch 132 is closed (turned on, short-circuited), thesecond terminal of the third capacitor 123 is electrically connected tothe second terminal of the fourth capacitor 124. When the second switch132 is open (turned off, open-circuited), the second terminal of thethird capacitor 123 is electrically isolated from the second terminal ofthe fourth capacitor 124.

A first terminal of a third switch 141 is electrically connected to thenode 11, and a second terminal of the third switch 141 is electricallyconnected to the node 14. In some embodiments, the third switch 141 iscontrollable by an electrical signal. In some embodiments, the thirdswitch 141 is an N-type metal-oxide semiconductor (NMOS) transistor, aP-type metal-oxide-semiconductor (PMOS) transistor, a pass gate, or thelike. When the third switch 141 is closed (turned on, short-circuited),the second terminal of the first capacitor 121 is electrically connectedto the second terminal of the fourth capacitor 124. When the thirdswitch 141 is open (turned off, open-circuited), the second terminal ofthe first capacitor 121 is electrically isolated from the secondterminal of the fourth capacitor 124.

A first terminal of a fourth switch 142 is electrically connected to thenode 12, and a second terminal of the fourth switch 142 is electricallyconnected to the node 14. In some embodiments, the fourth switch 142 iscontrollable by an electrical signal. In some embodiments, the fourthswitch 142 is an N-type metal-oxide semiconductor (NMOS) transistor, aP-type metal-oxide-semiconductor (PMOS) transistor, a pass gate, or thelike. When the fourth switch 142 is closed (turned on, short-circuited),the second terminal of the third capacitor 123 is electrically connectedto the second terminal of the second capacitor 122. When the fourthswitch 142 is open (turned off, open-circuited), the second terminal ofthe third capacitor 123 is electrically isolated from the secondterminal of the second capacitor 122.

In some embodiments, the first capacitor 121, the second capacitor 122,the third capacitor 123, and the fourth capacitor 124 are integratedcapacitors, such as metal-oxide-metal (MOM) capacitors,metal-insulator-metal (MIM) capacitors, polysilicon capacitors, or thelike.

FIG. 4 is a diagram of the variable capacitor 311 having the firstcapacitance in accordance with various embodiments of the presentdisclosure. FIG. 5 is a diagram of the variable capacitor 311 having thesecond capacitance in accordance with various embodiments of the presentdisclosure. In FIG. 4, the first switch 131 is closed, the second switch132 is closed, the third switch 141 is open, and the fourth switch 142is open. In this configuration, the capacitance C₃₁₁ of the variablecapacitor 311 is given by the following formula:

$\begin{matrix}{C_{311} = {\frac{C_{A}}{2} + \frac{C_{B}}{2}}} & (1)\end{matrix}$

where C_(A) is capacitance of the first capacitor 121 and capacitance ofthe second capacitor 122, and C_(B) is capacitance of the thirdcapacitor 123 and capacitance of the fourth capacitor 124.

In FIG. 5, the first switch 131 is open, the second switch 132 is open,the third switch 141 is closed, and the fourth switch 142 is closed. Inthis configuration, the capacitance C₃₁₁ of the variable capacitor 311is given by the following formula:

$\begin{matrix}{C_{311} = \frac{2C_{A}C_{B}}{C_{A} + C_{B}}} & (2)\end{matrix}$

Based on formula (1) and formula (2), the capacitance delta (ΔC) of thevariable capacitor 311 is given by the following formula:

$\begin{matrix}{{\Delta\; C} = \frac{\left( {C_{B} - C_{A}} \right)^{2}}{2\left( {C_{B} + C_{A}} \right)}} & (3)\end{matrix}$

Assuming C_(B) is n times C_(A), formula (3) can be rewritten in termsof n as:

$\begin{matrix}{{\Delta\; C} = {\frac{\left( {n - 1} \right)^{2}}{2\left( {n + 1} \right)}C_{A}}} & (4)\end{matrix}$

Using formula (4), it can be seen that for C_(A) of 1 fF and n of 1.2(C_(B)=1.2 fF), the capacitance delta ΔC is approximately 9.1 aF.

FIGS. 6 and 7 are diagrams of switch circuits 600, 700 in accordancewith various embodiments of the present disclosure. The switch circuit600 has inverted operation relative to the switch circuit 700. Forexample, when the switch circuit 600 is turned on, the switch circuit700 is turned off. In some embodiments, the switch circuit 600 is usedas the switches 131, 132 of the variable capacitor 311, and the switchcircuit 700 is used as the switches 141, 142 of the variable capacitor311. As such, nodes 61 and 62 may correspond to nodes 11 and 12 (ornodes 13 and 14), respectively. Nodes 71 and 72 may correspond to nodes11 and 14 (or nodes 13 and 12), respectively.

A switch control signal S6 controls turning on or turning off of theswitch circuit 600. A first inverter 151 of the switch circuit 600receives the switch control signal S6, and inverts the switch controlsignal S6 to output an inverted switch control signal at an outputterminal of the first inverter 151. A second inverter 152 receives theinverted switch control signal at an input terminal of the secondinverter 152, and inverts the inverted switch control signal to output asignal having the same logical polarity as the switch control signal S6at an output terminal of the second inverter 152. A switching transistor171 is an NMOS transistor in some embodiments, and has a gate electrodeelectrically connected to the output terminal of the first inverter 151for receiving the inverted switch control signal. A first resistor 161has a first terminal electrically connected to the output terminal ofthe second inverter 152. A second terminal of the first resistor 161 iselectrically connected to a source electrode of the switching transistor171 (e.g., at the node 61). A second resistor 162 has a first terminalelectrically connected to the output terminal of the second inverter152. A second terminal of the second resistor 162 is electricallyconnected to a drain electrode of the switching transistor 171 (e.g., atthe node 62). The first resistor 161 and the second resistor 162 act asalternating current (AC) chokes. In some embodiments, the first resistor161 has impedance much greater than drain-source resistance (R_(DS)) ofthe transistor 171. For example, resistance of the first resistor 161may be 10, 100, or 1000 times the drain-source resistance of thetransistor 171. In some embodiments, the second resistor 162 hasimpedance much greater than the drain-source resistance (R_(DS)) of thetransistor 171. For example, resistance of the second resistor 162 maybe 10, 100, or 1000 times the drain-source resistance of the transistor171. In some embodiments, the resistance of the first resistor 161 issubstantially the same as the resistance of the second resistor 162. Insome embodiments, an integrated inductor is used in place of, or inaddition to, the first resistor 161 or the second resistor 162. In someembodiments, the first resistor 161 and the second resistor 162 arepolysilicon resistors, titanium-nitride (TiN) resistors, or the like.

A switch control signal S7 controls turning on or turning off of theswitch circuit 700. A first inverter 153 of the switch circuit 700receives the switch control signal S7, and inverts the switch controlsignal S7 to output an inverted switch control signal at an outputterminal of the first inverter 153. A second inverter 154 receives theinverted switch control signal at an input terminal of the secondinverter 154, and inverts the inverted switch control signal to output asignal having the same logical polarity as the switch control signal S7at an output terminal of the second inverter 154. A switching transistor172 is a PMOS transistor in some embodiments, and has a gate electrodeelectrically connected to the output terminal of the first inverter 153for receiving the inverted switch control signal. A first resistor 163has a first terminal electrically connected to the output terminal ofthe second inverter 154. A second terminal of the first resistor 163 iselectrically connected to a source electrode of the switching transistor172 (e.g., at the node 71). A second resistor 164 has a first terminalelectrically connected to the output terminal of the second inverter154. A second terminal of the second resistor 164 is electricallyconnected to a drain electrode of the switching transistor 172 (e.g., atthe node 72). The first resistor 163 and the second resistor 164 act asalternating current (AC) chokes. In some embodiments, the first resistor163 has impedance much greater than drain-source resistance (R_(DS)) ofthe transistor 172. For example, resistance of the first resistor 163may be 10, 100, or 1000 times the drain-source resistance of thetransistor 172. In some embodiments, the second resistor 164 hasimpedance much greater than the drain-source resistance (R_(DS)) of thetransistor 172. For example, resistance of the second resistor 164 maybe 10, 100, or 1000 times the drain-source resistance of the transistor172. In some embodiments, the resistance of the first resistor 163 issubstantially the same as the resistance of the second resistor 164. Insome embodiments, an integrated inductor is used in place of, or inaddition to, the first resistor 163 or the second resistor 164. In someembodiments, the first resistor 163 and the second resistor 164 arepolysilicon resistors, titanium-nitride (TiN) resistors, or the like.

FIGS. 8, 9, 10 and 11 are diagrams of operating modes of the switchcircuits 600, 700 in accordance with various embodiments of the presentdisclosure. In some embodiments, the switch control signal S6 and theswitch control signal S7 are the same signal, or have the same logicalpolarity. As shown in FIG. 8, the switch control signals S6, S7 have thelogical polarity 0 (e.g., low voltage). As a result, the gate electrodeof the transistor 171 has the logical polarity 1 (e.g., high voltage),and the source and drain electrodes of the transistor 171 have thelogical polarity 0 (e.g., low voltage). Positive gate-source voltage(V_(GS)) of the transistor 171 turns on the transistor 171, electricallyconnecting the node 61 to the node 62 of the switch circuit 600. In theswitch circuit 700, the gate electrode of the transistor 172 has thelogical polarity 1 (e.g., high voltage) when the switch control signalS7 has the logical polarity 0 (e.g., low voltage). The source and drainelectrodes of the transistor 172 have the logical polarity 0 (e.g., lowvoltage). Negative source-gate voltage (V_(SG)) of the transistor 172turns off the transistor 172, electrically isolating the node 71 fromthe node 72 of the switch circuit 700.

As shown in FIG. 9, the switch control signals S6, S7 have the logicalpolarity 1 (e.g., high voltage). As a result, the gate electrode of thetransistor 171 has the logical polarity 0 (e.g., low voltage), and thesource and drain electrodes of the transistor 171 have the logicalpolarity 1 (e.g., high voltage). Negative gate-source voltage (V_(GS))of the transistor 171 turns off the transistor 171, electricallyisolating the node 61 from the node 62 of the switch circuit 600. In theswitch circuit 700, the gate electrode of the transistor 172 has thelogical polarity 0 (e.g., low voltage) when the switch control signal S7has the logical polarity 1 (e.g., high voltage). The source and drainelectrodes of the transistor 172 have the logical polarity 1 (e.g., highvoltage). Positive source-gate voltage (V_(SG)) of the transistor 172turns off the transistor 172, electrically connecting the node 71 to thenode 72 of the switch circuit 700.

In FIGS. 10 and 11, an NMOS transistor 173 is used in the switch circuit700 instead of the transistor 172 (PMOS) shown in FIG. 7. A gateelectrode of the NMOS transistor 173 is electrically connected to theoutput terminal of the first inverter 153. A source electrode of theNMOS transistor 173 is electrically connected to the node 71, and adrain electrode of the NMOS transistor 173 is electrically connected tothe node 72. In some embodiments, the transistors 171 and 173 are PMOStransistors. The transistors 171, 173 are of the same doping polarity(N-type, P-type). The transistors 171, 172 are of different dopingpolarities.

In FIG. 10, the switch control signal S7 has the logical polarity 1(e.g., high voltage) when the switch control signal S6 has the logicalpolarity 0 (e.g., low voltage). As a result, the gate electrode of thetransistor 171 has the logical polarity 1 (e.g., high voltage) due toinverting action of the first inverter 151, and the source and drainelectrodes of the transistor 171 have the logical polarity 0 (e.g., lowvoltage) due to the inverting action of the second inverter 152. Thetransistor 171 is turned on due to positive gate-source voltage (V_(GS))of the transistor 171, which electrically connects the node 61 to thenode 62 in the switch circuit 600. The switch control signal S7 has thelogical polarity 1 (e.g., high voltage). As a result, the gate electrodeof the NMOS transistor 173 has the logical polarity 0 (e.g., lowvoltage) due to inverting action of the first inverter 153, and thesource and drain electrodes of the NMOS transistor 173 have the logicalpolarity 1 (e.g., high voltage) due to the inverting action of thesecond inverter 154. The NMOS transistor 173 is turned off due tonegative gate-source voltage (V_(GS)) of the NMOS transistor 173, whichelectrically isolates the node 71 from the node 72 in the switch circuit700.

In FIG. 11, the switch control signal S7 has the logical polarity 0(e.g., low voltage) when the switch control signal S6 has the logicalpolarity 1 (e.g., high voltage). As a result, the gate electrode of thetransistor 171 has the logical polarity 0 (e.g., low voltage) due toinverting action of the first inverter 151, and the source and drainelectrodes of the transistor 171 have the logical polarity 1 (e.g., highvoltage) due to the inverting action of the second inverter 152. Thetransistor 171 is turned off due to negative gate-source voltage(V_(GS)) of the transistor 171, which electrically isolates the node 61from the node 62 in the switch circuit 600. The switch control signal S7has the logical polarity 0 (e.g., low voltage). As a result, the gateelectrode of the NMOS transistor 173 has the logical polarity 1 (e.g.,high voltage) due to inverting action of the first inverter 153, and thesource and drain electrodes of the NMOS transistor 173 have the logicalpolarity 0 (e.g., low voltage) due to the inverting action of the secondinverter 154. The NMOS transistor 173 is turned on due to positivegate-source voltage (V_(GS)) of the NMOS transistor 173, whichelectrically connects the node 71 to the node 72 in the switch circuit700.

FIG. 12 is a flowchart of a method 20 of operating an electronic devicewith switched-capacitor tuning in accordance with various embodiments ofthe present disclosure. In some embodiments, the method 20 operates theelectronic device 10. The following description of the method 20 is madewith reference to the electronic device 10 and the FIGS. 1-11 describedabove. In block 200, a first capacitor, such as the first capacitor 121,is provided. The first capacitor has a first terminal electricallyconnected to a first terminal of a third capacitor, such as the thirdcapacitor 123. In block 210, a second capacitor, such as the secondcapacitor 122, is provided. The second capacitor has a first terminalelectrically connected to a first terminal of a fourth capacitor, suchas the fourth capacitor 124.

In block 220, a first switch, such as the first switch 131, is turned onin a first period to electrically connect a second terminal of the firstcapacitor to a second terminal of the second capacitor. In block 230, asecond switch, such as the second switch 132, is turned on in the firstperiod to electrically connect a second terminal of the third capacitorto a second terminal of the fourth capacitor. In some embodiments,completion of the blocks 220 and 230 results in the variable capacitor311 configuration shown in FIG. 4. In some embodiments, the blocks 220and 230 are performed simultaneously.

In block 240, a third switch, such as the third switch 141, is turned onin a second period to electrically connect the second terminal of thefirst capacitor to the second terminal of the fourth capacitor. In block250, a fourth switch, such as the fourth switch 142, is turned on in thesecond period to electrically connect the second terminal of the thirdcapacitor to the second terminal of the second capacitor. In someembodiments, completion of the blocks 240 and 250 results in thevariable capacitor 311 configuration shown in FIG. 6. In someembodiments, the blocks 240 and 250 are performed simultaneously. Insome embodiments, the blocks 220 and 230 are performed by the switchcircuit 600 shown in FIG. 6, and the block 230 is performed by theswitch circuit 700 shown in FIG. 7. In some embodiments, the blocks 240and 250 are performed by the switch circuit 700 shown in FIG. 7.

In some embodiments, the block 220 further includes turning off thethird switch to electrically isolate the second terminal of the firstcapacitor from the second terminal of the fourth capacitor. In someembodiments, the block 230 further includes turning off the fourthswitch to electrically isolate the second terminal of the thirdcapacitor from the second terminal of the second capacitor.

In some embodiments, the block 240 further includes turning off thefirst switch to electrically isolate the second terminal of the firstcapacitor from the second terminal of the second capacitor. In someembodiments, the block 250 further includes turning off the secondswitch to electrically isolate the second terminal of the thirdcapacitor from the second terminal of the fourth capacitor.

FIG. 13 is a circuit diagram of a digitally-controlled oscillator (DCO)30 in accordance with various embodiments of the present disclosure. TheDCO 30 is operable over a range of frequencies from a minimum frequencyf_(min) to a maximum frequency f_(max). Transistors 321, 322 of the DCO30 are biased by a current source 340, and electrically connected to aresonant load including a capacitor bank 330 and inductors 301, 302 tiedto a voltage supply node VDD. In some embodiments, the transistors 321,322 are NMOS transistors.

A finite number of intermediate frequencies between the minimumfrequency f_(min) and the maximum frequency f_(max) are selectablethrough digital control of the capacitor bank 330 by a controller 350.The capacitor bank 330 has variable capacitance controllable by controlsignals 351, 352, 353, . . . , 354 of the controller 350. In someembodiments, when the control signals 351, 352, 353, . . . , 354outputted by the controller 350 to the capacitor bank 330 all have afirst logical polarity (e.g., logic 0, logic low), operating frequencyof the DCO 30 is the minimum frequency f_(min). In some embodiments,when the control signals 351, 352, 353, . . . , 354 all have a secondlogic polarity (e.g., logic 1, logic high), the operating frequency ofthe DCO 30 is the maximum frequency f_(max).

In some embodiments, each capacitor of capacitors 331, 332, 333, . . . ,334 is a variable capacitor similar to, or identical to, the variablecapacitor 311. Each capacitor of the capacitors 331, 332, 333, . . . ,334 is associated with a first capacitance (e.g., C₀ _(—) ₃₃₁, C₀ _(—)₃₃₂) and a second capacitance (e.g., C₁ _(—) ₃₃₁, C₁ _(—) ₃₃₂). Eachcapacitor of the capacitors 331, 332, 333, . . . , 334 is associatedwith a capacitance delta. For example, the capacitor 331 is associatedwith a capacitance delta equal to C₁ _(—) ₃₃₁−C₀ _(—) ₃₃₁. A unitcapacitance delta may be defined as ΔC. The capacitors 331, 332, 333, .. . , 334 of the capacitor bank 330 have the same or differentcapacitance values (or capacitance deltas). In some embodiments, a firstgroup of the capacitors 331, 332, 333, . . . , 334 have binary-codedcapacitance deltas (e.g., 16*ΔC, 8*ΔC, 4*ΔC), and a second group of thecapacitors 331, 332, 333, . . . , 334 have thermometer-coded capacitancedeltas (e.g., ΔC, ΔC, ΔC).

The capacitor bank 330 and inductors 301, 302 form a resonator whoseoscillation frequency is given by:

$\begin{matrix}{\omega_{osc} = \frac{1}{\sqrt{L \cdot \left( {C_{m\; i\; n} + {{n \cdot \Delta}\; C}} \right)}}} & (5)\end{matrix}$

where L is the sum of the inductances of the inductors 301 and 302,C_(min) is minimum (baseline) capacitance of the capacitor bank 330(e.g., C₀ _(—) ₃₃₁+C₀ _(—) ₃₃₂+ . . . +C₀ _(—) ₃₃₄), ΔC is the unitcapacitance delta, and n is a number from 0 to N, where N is number ofthe capacitors 331, 332, 333, . . . , 334 in the capacitor bank 330. Amaximum capacitance C_(max) of the capacitor bank 330 is, then, equal toC_(min)+N*ΔC.

In some embodiments, the controller 350 dynamically controls thecapacitance of the capacitor bank 330. In some embodiments, thecontroller 350 receives an input signal from an external circuit, andvaries the capacitance of the capacitor bank 330 based on the inputsignal. In some embodiments, the DCO 30 is in an all-digitalphase-locked loop (ADPLL), and the controller 350 receives a phase orfrequency error signal from a detector circuit of the ADPLL. The errorsignal indicates whether a clock signal outputted by the DCO 30 shouldbe sped up (increase oscillation frequency) or slowed down (decreaseoscillation frequency) to achieve a phase or frequency lock with anexternal clock signal. If the oscillation frequency of the DCO 30 is tobe increased, the controller 350 adjusts the control signals 351, 352,353, . . . , 354 to decrease the capacitance of the capacitor bank 330.If the oscillation frequency of the DCO 30 is to be decreased, thecontroller 350 adjusts the control signals 351, 352, 353, . . . , 354 toincrease the capacitance of the capacitor bank 330.

In some embodiments, the controller 350 statically controls thecapacitance of the capacitor bank 330. In some embodiments, thecapacitor bank 330 and the controller 350 are applied to a tunableamplifier instead of to the DCO 30. In a functional test phase ofdevelopment of an integrated circuit die including the tunableamplifier, a parameter of the tunable amplifier, such as gain,bandwidth, linearity or the like is characterized through testequipment. Based on the characterization, the controller 350 receives aprogramming signal for permanently setting logical polarities of thecontrol signals 351, 352, 353, . . . , 354. In some embodiments, a firstterminal of the capacitor bank 330 (e.g., the node 31 of FIG. 3) iselectrically connected to an input terminal of the tunable amplifier,and a second terminal of the capacitor bank 330 (e.g., the node 32 ofFIG. 3) is electrically connected to an output terminal of the tunableamplifier. In some embodiments, the controller 350 includes a bank offuses corresponding to the control signals 351, 352, 353, . . . , 354.To set the logical polarities, the fuses are selectively blown orpreserved to set the control signals 351, 352, 353, . . . , 354 to havelogic high or logic low polarities.

FIG. 14 is a flowchart of a method 40 of manufacturing an electronicdevice with switched-capacitor tuning in accordance with variousembodiments of the present disclosure. In some embodiments, the method40 manufactures an integrated circuit (IC) die including adigitally-controllable capacitor bank, such as the capacitor bank 330,and a controller, such as the controller 350. In some embodiments, themethod 40 is performed partially or fully in an electronic designautomation (EDA) environment run on a physical server. The physicalserver includes at least a processing unit and a memory unit. In block400, a minimum frequency and a maximum frequency of a resonatorincluding the capacitor bank are determined. In some embodiments, theminimum frequency and the maximum frequency are inputted to the physicalserver by a user through an input device, such as a mouse or a keyboard.In block 410, resolution of intermediate frequencies between the minimumand maximum frequencies is determined. In some embodiments, theresolution is a number of the intermediate frequencies. In someembodiments, the resolution is a frequency step or delta of theintermediate frequencies. In some embodiments, the user selects thenumber in a graphical user interface of the EDA environment, through adrop-down box, a radio button, or the like. In some embodiments, thefrequency step is calculated by the server according to the number.

In block 420, an inductor type and an inductance of an inductive element(e.g., an inductor) are set according to the minimum and maximumfrequencies and a quality factor (Q). In some embodiments, the inductortype is selected from a library of inductor models, and parameters of aninductor model are entered by the user to set the inductance and Q of aninductor. Examples of inductor types include planar spiral inductors,toroidal-meander type integrated (TMTI) inductors, solenoid-typeintegrated inductors (SI2's), or the like.

Variable capacitors of the capacitor bank, such as the variablecapacitor 311, have two capacitances alternately selected throughdigital control (e.g., a 1-bit control signal). First and secondcapacitances (e.g., minimum and maximum capacitances) of the variablecapacitors are determined in block 430 according to the minimum andmaximum frequencies, the resolution, and the inductance of the inductiveelement. In some embodiments, the block 430 is performed automaticallyby the server. For example, when the user enters values for the minimumfrequency, the maximum frequency, the number of intermediatefrequencies, and the inductance of the inductive element, the server maycalculate the first and second capacitances of the variable capacitorsassociated with the values entered. For example, a frequency range iscalculated by taking the difference of the maximum frequency and theminimum frequency, and the frequency range is further divided intointermediate frequencies according to the resolution. In someembodiments, the user further specifies coding type of the variablecapacitors. In some embodiments, the coding type is binary orthermometer. Based on the coding types, capacitance deltas associatedwith each of the variable capacitors are calculated.

In block 440, capacitances of first, second, third, and fourthcapacitors (e.g., the first capacitor 121, the second capacitor 122, thethird capacitor 123, and the fourth capacitor 124 of the variablecapacitor 311) are set. In some embodiments, the capacitances are setaccording to the resolution set in the block 410. For example, an i^(th)variable capacitor of the variable capacitors may be associated with acapacitive delta ΔC_(i), such that:

$\begin{matrix}{{\Delta\; C_{i}} = \frac{\left( {C_{B} - C_{A}} \right)^{2}}{2\left( {C_{A} + C_{B}} \right)}} & (6)\end{matrix}$

which is similar to the formula (3) above. In some embodiments, thecapacitance C_(A) of the first and second capacitors is set to acapacitance of an integrated capacitor having minimum feature size in asemiconductor process node (e.g., 65 nanometers, 40 nanometers, 28nanometers, or the like).

In block 450, the capacitances of the first, second, third, and fourthcapacitors of the variable capacitors of the capacitor block have beenset, and the inductance of the inductive element has been set. Usinglayout tools, a circuit layout including the resonator having thecapacitor block and the inductive element is generated. After the blocks400-440 are completed, the method provides for producing anon-transitory computer readable storage media with instructions forbuilding a mask set for the IC die based on the circuit layoutcontaining the resonator including the capacitor block and the inductiveelement.

Embodiments may achieve advantages. The capacitor block 330 using thevariable capacitor 311 is able to achieve high frequency resolution withlittle to no area penalty through use of the switched-capacitor networkshown in FIG. 3.

FIG. 15 illustrates a diagram of a variable capacitor in accordance withvarious embodiments of the present disclosure. The variable capacitor1500 is between a first node OUT+ and a second node OUT− as shown inFIG. 15. The variable capacitor 1500 comprises four variable capacitanceblocks, namely a first variable capacitance block 1502, a secondvariable capacitance block 1504, a third variable capacitance block 1506and a fourth variable capacitance block 1508. The variable capacitor1500 further comprises four switches 1512, 1514, 1516 and 1518.

As shown in FIG. 15, the switch 1512 is coupled between the firstvariable capacitance block 1502 and the second variable capacitanceblock 1504. The switch 1514 is coupled between the third variablecapacitance block 1506 and the fourth variable capacitance block 1508.The switch 1516 is coupled between the first variable capacitance block1502 and the fourth variable capacitance block 1508. The switch 1518 iscoupled between the third variable capacitance block 1506 and the secondvariable capacitance block 1504.

In some embodiments, when switches 1512 and 1514 are turned on (orsimultaneously turned on), and switches 1516 and 1518 are turned off (orsimultaneously turned off), the first variable capacitance block 1502and the second variable capacitance block 1504 are connected in seriesthrough the turned-on switch 1512. The series-connected variablecapacitance blocks 1502 and 1504 form a first capacitor (a firstcapacitor branch). Likewise, the third variable capacitance block 1506and the fourth variable capacitance block 1508 are connected in seriesthrough the turned-on switch 1514. The series-connected variablecapacitance blocks 1506 and 1508 form a second capacitor (a secondcapacitor branch). The first capacitor and the second capacitor areconnected in parallel to form a first equivalent capacitor of thevariable capacitor 1500.

On the other hand, when switches 1512 and 1514 are turned off (orsimultaneously turned off), and switches 1516 and 1518 are turned on (orsimultaneously turned on), the first variable capacitance block 1502 andthe fourth variable capacitance block 1508 are connected in seriesthrough the turned-on switch 1516. The series-connected variablecapacitance blocks 1502 and 1508 form a third capacitor (a thirdcapacitor branch). Likewise, the third variable capacitance block 1506and the second variable capacitance block 1504 are connected in seriesthrough the turned-on switch 1518. The series-connected variablecapacitance blocks 1504 and 1506 form a fourth capacitor (a fourthcapacitor branch). The third capacitor and the fourth capacitor areconnected in parallel to form a second equivalent capacitor of thevariable capacitor 1500. By controlling the on-off of the switches ofFIG. 15, the variable capacitor 1500 may have at least two differentcapacitances. The operation principle of the variable capacitor 1500will be described in detail with respect to FIGS. 17 and 18.

In some embodiments, switches (e.g., switch 1512) shown in FIG. 15 maybe implemented as N-type metal-oxide semiconductor (NMOS) transistors,P-type metal-oxide-semiconductor (PMOS) transistors, pass gates, anycombinations thereof and/or the like.

In some embodiments, each variable capacitance block (e.g., the firstvariable capacitance block 1502) shown in FIG. 15 may be implemented asa combination of a plurality of capacitors. For example, the variablecapacitance block may be implemented as suitable capacitance structuressuch as the capacitance structures shown in FIG. 4 and FIG. 5.

In some embodiments, the first variable capacitance block 1502 maycomprise a plurality of first capacitors. The first capacitors arearranged in a first configuration. The second variable capacitance block1504 may comprise a plurality of second capacitors. The secondcapacitors are arranged in the first configuration. In some embodiments,the first configuration is the capacitor configuration shown in FIG. 4.In alternative embodiments, the first configuration is the capacitorconfiguration shown in FIG. 5.

In some embodiments, the third variable capacitance block 1506 maycomprise a plurality of third capacitors. The third capacitors arearranged in a second configuration. The fourth variable capacitanceblock 1508 may comprise a plurality of fourth capacitors. The fourthcapacitors are arranged in the second configuration. In someembodiments, the second configuration is the capacitor configurationshown in FIG. 4. In alternative embodiments, the second configuration isthe capacitor configuration shown in FIG. 5.

In some embodiments, each capacitor (not shown) of the variablecapacitance blocks (e.g., the first variable capacitance block 1502) maybe an integrated capacitor, such as metal-oxide-metal (MOM) capacitors,metal-insulator-metal (MIM) capacitors, polysilicon capacitors, anycombinations thereof and/or the like.

It should be noted that the variable capacitor 1500 can be used in thedigitally-controlled oscillator shown in FIG. 13. In other words, thecapacitors 331, 332, 333, . . . , 334 shown in FIG. 13 may be a variablecapacitor similar to, or identical to, the variable capacitor 1500 shownin FIG. 15. The operation principles of the digitally-controlledoscillator has been described above with respect to FIG. 13, and henceare not discussed again to avoid unnecessary repetition. Furthermore,the flowcharts shown in FIG. 12 and FIG. 14 are applicable to thevariable capacitor shown in FIG. 15.

It should further be noted that switches 1512, 1514, 1516 and 1518 shownin FIG. 15 are similar to those shown in FIG. 3. The detailed structuresand operation principles of these switches have been described abovewith respect to FIGS. 6-11, and hence are not discussed again forsimplicity.

FIG. 16 illustrates a schematic diagram of the variable capacitor shownin FIG. 15 in accordance with various embodiments of the presentapplication. The first variable capacitance block 1502 comprises fourcapacitors. The capacitor configuration of the first variablecapacitance block 1502 is similar to that shown in FIG. 5.

As shown in FIG. 16, a first capacitance of the first capacitor is equalto a second capacitance of the second capacitor. Both the firstcapacitance and the second capacitance are equal to C_(A). A thirdcapacitance of the third capacitor is equal to a fourth capacitance ofthe fourth capacitor. Both the third capacitance and the fourthcapacitance are equal to C_(B).

The first capacitor and the fourth capacitor are connected in seriesbetween a first terminal and a second terminal of the first variablecapacitance block 1502. The second capacitor and the third capacitor areconnected in series between the first terminal and the second terminalof the first variable capacitance block 1502. The equivalent capacitanceof the first variable capacitance block 1502 is given by the followingequation:

$\begin{matrix}{C_{1502} = \frac{2C_{A}C_{B}}{C_{A} + C_{B}}} & (7)\end{matrix}$

Assuming C_(A) and C_(B) satisfy the following equation:C _(B)=(1+Δ)·C _(A)  (8)where Δ is approximately equal to 0.1 in some embodiments.

After substituting C_(B) of Equation (7) with C_(B) of Equation (8),Equation (7) may be expressed as the following equation:

$\begin{matrix}{C_{1502} = {C_{A}\frac{2 + {2\;\Delta}}{2 + \Delta}}} & (9)\end{matrix}$

The second variable capacitance block 1504 comprises four capacitors.The capacitor configuration of the second variable capacitance block1504 is similar to that of the first variable capacitance block 1502,and hence is not described in further detail to avoid unnecessaryrepetition. The equivalent capacitance of the second variablecapacitance block 1504 is given by the following formula:

$\begin{matrix}{C_{1504} = \frac{2C_{A}C_{B}}{C_{A} + C_{B}}} & (10)\end{matrix}$

It should be noted that the capacitance of C₁₅₀₄ is equal to thecapacitance of C₁₅₀₂. Throughout the description, the capacitance ofC₁₅₀₂ and C₁₅₀₄ is alternatively referred to as C_(X) for simplicity.According to Equation (9), C_(X) can be given by the following equation:

$\begin{matrix}{C_{X} = {C_{A}\frac{2 + {2\Delta}}{2 + \Delta}}} & (11)\end{matrix}$

The third variable capacitance block 1506 comprises four capacitors. Thecapacitor configuration of the third variable capacitance block 1506 issimilar to that shown in FIG. 4, and hence is not described in furtherdetail to avoid unnecessary repetition. The equivalent capacitance ofthe third variable capacitance block 1506 is given by the followingequation:

$\begin{matrix}{C_{1506} = {\frac{C_{A}}{2} + \frac{C_{B}}{2}}} & (12)\end{matrix}$

After substituting C_(B) of Equation (12) with C_(B) of Equation (8),Equation (12) may be expressed as the following equation:

$\begin{matrix}{C_{1506} = {C_{A}\frac{2 + \Delta}{2}}} & (13)\end{matrix}$

The fourth variable capacitance block 1508 comprises four capacitors.The capacitor configuration of the fourth variable capacitance block1508 is similar to that of the third variable capacitance block 1506,and hence is not described in further detail to avoid unnecessaryrepetition. The equivalent capacitance of the fourth variablecapacitance block 1508 is given by the following equation:

$\begin{matrix}{C_{1508} = {\frac{C_{A}}{2} + \frac{C_{B}}{2}}} & (14)\end{matrix}$

It should be noted that the capacitance of C₁₅₀₆ is equal to thecapacitance of C₁₅₀₈. Throughout the description, the capacitance ofC₁₅₀₆ and C₁₅₀₈ is alternatively referred to as C_(//) for simplicity.According to Equation (13), C_(//) is given by the following equation:

$\begin{matrix}{C_{//} = {C_{A}\frac{2 + \Delta}{2}}} & (15)\end{matrix}$

Assuming C_(//) and C_(X) satisfy the following equation:C _(X)=(1+δ)·C _(//)  (16)

According to Equations (11) and (15), Equation (16) may be expressed as:

$\begin{matrix}{\delta = {{\frac{C_{X}}{C_{//}} - 1} = {\frac{C_{A}\frac{2 + {2\Delta}}{2 + \Delta}}{C_{A}\frac{2 + \Delta}{2}} - 1}}} & (17)\end{matrix}$

From Equation (17), δ can be rewritten as:

$\begin{matrix}{\delta = \frac{- \Delta^{2}}{4 + {4\Delta} + \Delta^{2}}} & (18)\end{matrix}$

Since Δ is approximately equal to 0.1, after ignoring high order terms,Equation (18) can be simplified as:

$\begin{matrix}{\delta = \frac{\Delta^{2}}{4}} & (19)\end{matrix}$

FIG. 17 illustrates a schematic diagram of the variable capacitor havingthe first capacitor in accordance with various embodiments of thepresent disclosure. As shown in FIG. 17, the switches 1512 and 1514 areturned on, and the switches 1516 and 1518 are turned off. The turned-onswitch 1512 connects the first variable capacitance block 1502 and thesecond variable capacitance block 1504 in series to form a firstcapacitor branch. Likewise, the turned-on switch 1514 connects the thirdvariable capacitance block 1506 and the fourth variable capacitanceblock 1508 in series to form a second capacitor branch. The firstcapacitor branch and the second capacitor branch are connected inparallel to form the first capacitor. The capacitance of the firstcapacitor can be defined as C_(parallel). C_(parallel) is given by thefollowing equation:

$\begin{matrix}{C_{parallel} = {\frac{C_{//}}{2} + \frac{C_{X}}{2}}} & (20)\end{matrix}$

After substituting Equation (16) into Equation (20), Equation (20) canbe expressed as the following equation:

$\begin{matrix}{C_{parallel} = {C_{//} \cdot \frac{2 + \delta}{2}}} & (21)\end{matrix}$

FIG. 18 illustrates a schematic diagram of the variable capacitor havingthe second capacitor in accordance with various embodiments of thepresent disclosure. As shown in FIG. 18, the switches 1516 and 1518 areturned on, and the switches 1512 and 1514 are turned off. The turned-onswitch 1516 connects the first variable capacitance block 1502 and thefourth variable capacitance block 1508 in series to form a thirdcapacitor branch. Likewise, the turned-on switch 1518 connects the thirdvariable capacitance block 1506 and the second variable capacitanceblock 1504 in series to form a fourth capacitor branch. The thirdcapacitor branch and the fourth capacitor branch are connected inparallel to form the second capacitor. The capacitance of the secondcapacitor can be defined as C_(cross). C_(cross) is given by thefollowing equation:

$\begin{matrix}{C_{cross} = \frac{2 \cdot C_{//} \cdot C_{X}}{C_{//} + C_{X}}} & (22)\end{matrix}$

After substituting Equation (16) into Equation (22), Equation (22) canbe expressed as the following equation:

$\begin{matrix}{C_{cross} = {C_{//} \cdot \frac{2 + {2\delta}}{2 + \delta}}} & (23)\end{matrix}$

In consideration with Equation (21) and Equation (23), the capacitancedelta of the variable capacitor 1500 is given by the following equation:

$\begin{matrix}{{\Delta\; C} = {{C_{parallel} - C_{cross}} = {C_{//} \cdot \left( {\frac{2 + \delta}{2} - \frac{2 + {2\delta}}{2 + \delta}} \right)}}} & (24)\end{matrix}$

Based upon Equation (24), the capacitance delta of the variablecapacitor 1500 can be simplified as:

$\begin{matrix}{{\Delta\; C} = {C_{//} \cdot \frac{\delta^{2}}{4 + {4\delta}}}} & (25)\end{matrix}$

Equation (25) can be approximated as:

$\begin{matrix}{\frac{\Delta\; C}{C_{//}} = {\frac{\delta^{2}}{4} = \frac{\Delta^{2}}{64}}} & (26)\end{matrix}$

As described above, Δ is approximately equal to 0.1. Equation (26) givesthe ratio of the capacitance delta to C// is approximately equal to1.56·10⁻⁶. One advantageous feature having the variable capacitor shownin FIGS. 15-18 is the variable capacitor 1500 can achieve a highresolution variable capacitance. In some embodiments, the capacitancevariation from a semiconductor process is about 0.1 fF. Based upon sucha capacitance variation (e.g., 0.1 fF), an oscillator (e.g., theoscillator shown in FIG. 13) may be capable of delivering an outputresolution of about 13 bits. The variable capacitor shown in FIG. 3 mayimprove the output resolution by reducing the capacitance variation to alevel approximately equal to 0.001 fF. Such a reduced capacitancevariation helps the oscillator shown in FIG. 13 achieve an outputresolution of about 19 bits.

The variable capacitor 1500 further reduces the capacitance variation asshown in Equation (26). The variable capacitor 1500 can improve theoutput resolution of the oscillator shown in FIG. 13 by 4 or 5 bits. Asa result, an oscillator (e.g., the oscillator shown in FIG. 13)comprising variable capacitors 1500 can achieve an output resolution ofabout 24 bits. Such a resolution satisfies the frequency resolutionrequirements of 4G and/or 5G wireless communication systems.

Circuits are typically powered and/or biased by multiple voltages. Themultiple voltages set up potential differences that allow electricalcurrents to flow throughout the circuit to perform various functions.Typically, electrical currents are defined as flowing from high voltageto low voltage. Voltage sources in circuits are also often defined interms of a supply voltage and ground, with ground representing 0 Volts.Other definitions are sometimes given in terms of an upper supplyvoltage (VDD, VCC), and a lower supply voltage (VSS, VEE). Thus, acircuit that operates on a 1.8 Volt supply may be defined as having anupper bias of 0.9 Volts, and a lower bias of −0.9 Volts. In thefollowing description, the term “ground” should be interpreted asincluding low supply voltage, such as the −0.9 Volts in the previousexample, unless specifically referred to as “earth ground,” or the like.Voltage levels, being relative, are not then intended so much to limitthe scope of the disclosure, but more as a point of reference forconvenient illustration.

Metal-oxide-semiconductor (MOS) transistors are typically described interms of four transistor terminals: a gate, a source, a drain, and abulk. It should be appreciated that most MOS transistors are symmetricaldevices, such that the source and the drain thereof are interchangeable,and the terms “source” and “drain” often represent nomenclature forconvenience of discussion. Terminals of MOS transistors may also bereferred to as “electrodes,” “ends,” and the like, without anydistinction intended through use of these different names. Biasing ofsuch terminals is usually performed through direct or indirect contactbetween a direct current (DC) voltage source and the terminal beingbiased. The contact may be through metallization layers, contact vias,pads, bumps, and/or similar interconnect structures formed on and overdevice regions of the MOS transistors.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB or both A and B. Furthermore, to the extent that “includes”, “having”,“has”, “with”, or variants thereof are used in either the detaileddescription or the claims, such terms are intended to be inclusive in amanner similar to the term “comprising”.

Although the present embodiments and their advantages have beendescribed in detail, it should be understood that various changes,substitutions, and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. Moreover, the scope of the present application is not intendedto be limited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods, and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

In accordance with an embodiment, a device comprises an inductiveelement and a variable capacitor connected in parallel with theinductive element, wherein the variable capacitor comprises a firstvariable capacitance block comprising a plurality of first capacitors,and wherein the first capacitors are arranged in a first configuration,a second variable capacitance block comprising a plurality of secondcapacitors, and wherein the second capacitors are arranged in the firstconfiguration, a third variable capacitance block comprising a pluralityof third capacitors, and wherein the third capacitors are arranged in asecond configuration, a fourth variable capacitance block comprising aplurality of fourth capacitors, and wherein the fourth capacitors arearranged in the second configuration, a first switch coupled between thefirst variable capacitance block and the second variable capacitanceblock, a second switch coupled between the third variable capacitanceblock and the fourth variable capacitance block, a third switch coupledbetween the first variable capacitance block and the fourth variablecapacitance block and a fourth switch coupled between the third variablecapacitance block and the second variable capacitance block.

In accordance with an embodiment, a device comprises a first variablecapacitance block comprising four first capacitors, a second variablecapacitance block comprising four second capacitors, wherein the secondcapacitors are arranged in a same configuration as the first capacitors,a third variable capacitance block comprising four third capacitors, afourth variable capacitance block comprising four fourth capacitors, andwherein the fourth capacitors are arranged in a same configuration asthe third capacitors, a first switch coupled between the first variablecapacitance block and the second variable capacitance block, a secondswitch coupled between the third variable capacitance block and thefourth variable capacitance block, a third switch coupled between thefirst variable capacitance block and the fourth variable capacitanceblock and a fourth switch coupled between the third variable capacitanceblock and the second variable capacitance block.

In accordance with an embodiment, a method comprises providing a firstvariable capacitance block comprising four first capacitors, a secondvariable capacitance block comprising four second capacitors, a thirdvariable capacitance block comprising four third capacitors and a fourthvariable capacitance block comprising four fourth capacitors, whereinthe first variable capacitance block and the second variable capacitanceblock are of a first capacitor configuration and the third variablecapacitance block and the fourth variable capacitance block are of asecond capacitor configuration, connecting the first variablecapacitance block with the second variable capacitance block through afirst switch, connecting the third variable capacitance block with thefourth variable capacitance block through a second switch, connectingthe first variable capacitance block with the fourth variablecapacitance block through a third switch and connecting the thirdvariable capacitance block with the second variable capacitance blockthrough a fourth switch.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: an inductive element; and avariable capacitor connected in parallel with the inductive element,wherein the variable capacitor comprises: a first variable capacitanceblock comprising a plurality of first capacitors, and wherein the firstcapacitors are arranged in a first configuration; a second variablecapacitance block comprising a plurality of second capacitors, andwherein the second capacitors are arranged in the first configuration; athird variable capacitance block comprising a plurality of thirdcapacitors, and wherein the third capacitors are arranged in a secondconfiguration; a fourth variable capacitance block comprising aplurality of fourth capacitors, and wherein the fourth capacitors arearranged in the second configuration; a first switch coupled between thefirst variable capacitance block and the second variable capacitanceblock; a second switch coupled between the third variable capacitanceblock and the fourth variable capacitance block; a third switch coupledbetween the first variable capacitance block and the fourth variablecapacitance block; and a fourth switch coupled between the thirdvariable capacitance block and the second variable capacitance block. 2.The device of claim 1, wherein: the first variable capacitance blockcomprises a first capacitor, a second capacitor, a third capacitor and afourth capacitor, and wherein: a first capacitance of the firstcapacitor is equal to a second capacitance of the second capacitor; athird capacitance of the third capacitor is equal to a fourthcapacitance of the fourth capacitor; the first capacitor and the fourthcapacitor are connected in series between a first terminal and a secondterminal of the first variable capacitance block; and the secondcapacitor and the third capacitor are connected in series between thefirst terminal and the second terminal of the first variable capacitanceblock.
 3. The device of claim 2, wherein: the third variable capacitanceblock comprises a fifth capacitor, a sixth capacitor, a seventhcapacitor and an eighth capacitor, and wherein: a fifth capacitance ofthe fifth capacitor is equal to a sixth capacitance of the sixthcapacitor; a seventh capacitance of the seventh capacitor is equal to aneighth capacitance of the eighth capacitor; the fifth capacitor and thesixth capacitor are connected in series between a first terminal and asecond terminal of the third variable capacitance block; and the seventhcapacitor and the eighth capacitor are connected in series between thefirst terminal and the second terminal of the third variable capacitanceblock.
 4. The device of claim 3, wherein: the first capacitance is equalto the fifth capacitance; and the third capacitance is equal to theseventh capacitance.
 5. The device of claim 2, wherein: a ratio of thefirst capacitance to the third capacitance is approximately equal to1.1.
 6. The device of claim 5, wherein: the first switch and the secondswitch are turned on simultaneously; and the third switch and the fourthswitch are turned off simultaneously.
 7. The device of claim 5, wherein:the third switch and the fourth switch are turned on simultaneously; andthe first switch and the second switch are turned off simultaneously. 8.A device comprising: a first variable capacitance block comprising fourfirst capacitors; a second variable capacitance block comprising foursecond capacitors, wherein the second capacitors are arranged in a sameconfiguration as the first capacitors; a third variable capacitanceblock comprising four third capacitors; a fourth variable capacitanceblock comprising four fourth capacitors, and wherein the fourthcapacitors are arranged in a same configuration as the third capacitors;a first switch coupled between the first variable capacitance block andthe second variable capacitance block; a second switch coupled betweenthe third variable capacitance block and the fourth variable capacitanceblock; a third switch coupled between the first variable capacitanceblock and the fourth variable capacitance block; and a fourth switchcoupled between the third variable capacitance block and the secondvariable capacitance block.
 9. The device of claim 8, wherein the firstvariable capacitance block comprises: a first functional blockcomprising two capacitors connected in series, and wherein the twocapacitors of the first functional block have different capacitances;and a second functional block comprising two capacitors connected inseries, and wherein the two capacitors of the second functional blockhave different capacitances, and wherein the first functional block andthe second functional block are connected in parallel.
 10. The device ofclaim 8, wherein the third variable capacitance block comprises: a thirdfunctional block comprising two capacitors connected in series, andwherein the two capacitors of the third functional block have a firstcapacitance; and a fourth functional block comprising two capacitorsconnected in series, and wherein the two capacitors of the fourthfunctional block have a second capacitance, and wherein the thirdfunctional block and the fourth functional block are connected inparallel.
 11. The device of claim 10, wherein: the first capacitance isapproximately equal to 1.1 times the second capacitance.
 12. The deviceof claim 8, wherein: the first switch, the second switch, the thirdswitch and the fourth switch are arranged such that: in a firstoperation mode, the first variable capacitance block and the secondvariable capacitance block are connected in series to form a firstcapacitor branch, and the third variable capacitance block and thefourth variable capacitance block are connected in series to form asecond capacitor branch, and wherein the first capacitor branch and thesecond capacitor branch are connected in parallel; and in a secondoperation mode, the first variable capacitance block and the fourthvariable capacitance block are connected in series to form a thirdcapacitor branch, and the third variable capacitance block and thesecond variable capacitance block are connected in series to form afourth capacitor branch, and wherein the third capacitor branch and thefourth capacitor branch are connected in parallel.
 13. The device ofclaim 12, wherein: in the first operation mode, the first variablecapacitance block, the second variable capacitance block, the thirdvariable capacitance block and the fourth variable capacitance blockform a first equivalent capacitor; and in the second operation mode, thefirst variable capacitance block, the second variable capacitance block,the third variable capacitance block and the fourth variable capacitanceblock form a second equivalent capacitor.
 14. A method comprising:providing a first variable capacitance block comprising four firstcapacitors, a second variable capacitance block comprising four secondcapacitors, a third variable capacitance block comprising four thirdcapacitors and a fourth variable capacitance block comprising fourfourth capacitors, wherein: the first variable capacitance block and thesecond variable capacitance block are of a first capacitorconfiguration; and the third variable capacitance block and the fourthvariable capacitance block are of a second capacitor configuration;connecting the first variable capacitance block with the second variablecapacitance block through a first switch; connecting the third variablecapacitance block with the fourth variable capacitance block through asecond switch; connecting the first variable capacitance block with thefourth variable capacitance block through a third switch; and connectingthe third variable capacitance block with the second variablecapacitance block through a fourth switch.
 15. The method of claim 14,further comprising: in response to a first operation mode, turning onthe first switch and the second switch; and turning off the third switchand the fourth switch.
 16. The method of claim 15, wherein: in the firstoperation mode, the first variable capacitance block and the secondvariable capacitance block are connected in series to form a firstcapacitor branch; and the third variable capacitance block and thefourth variable capacitance block are connected in series to form asecond capacitor branch, and wherein the first capacitor branch and thesecond capacitor branch are connected in parallel.
 17. The method ofclaim 14, further comprising: in response to a second operation mode,turning off the first switch and the second switch; and turning on thethird switch and the fourth switch.
 18. The method of claim 17, wherein:in the second operation mode, the first variable capacitance block andthe fourth variable capacitance block are connected in series to form athird capacitor branch; and the third variable capacitance block and thesecond variable capacitance block are connected in series to form afourth capacitor branch, and wherein the third capacitor branch and thefourth capacitor branch are connected in parallel.
 19. The method ofclaim 14, further comprising: connecting a first element having a firstcapacitance with a fourth element having a second capacitance; andconnecting a second element having the first capacitance with a thirdelement having the second capacitance, wherein the first element, thesecond element, the third element and the fourth element form the firstcapacitor configuration.
 20. The method of claim 14, further comprising:connecting a first element having a first capacitance with a secondelement having the first capacitance; and connecting a third elementhaving a second capacitance with a fourth element having the secondcapacitance, wherein the first element, the second element, the thirdelement and the fourth element form the second capacitor configuration.